The present invention relates to an unique method for preparing N-substituted-N'-phenyl-p-phenylenediamines from a mixture of N-phenyl-p-quinoneimine and p-hydroxydiphenylamine. N-substituted-N'-phenyl-p-phenylenediamines are useful as in the production of drugs, agricultural products, and useful as dyes, antioxidants, antiozonants, gel inhibitors and polymerization inhibitors for rubber.
N-substituted-N'-phenyl-p-phenylenediamines have been made by a variety of methods known to those skilled in the art. For example, Japanese Application 125343-1981 discloses a process for the preparation of phenylenediamines or its N-substitution product by reacting aminophenol or its N-substitution product with (a) ammonia, primary amine or secondary amine in the presence of an acidic catalyst and polycyclic aromatic compound. The process disclosed in Japanese Application No. 125343-1981 is characterized by a one step, one pot procedure and suggests via gas chromatography that yields are upwards to 50 percent. However, preparation of the products by this procedure would necessitate the use of elaborate distillation equipment to remove the polycyclic aromatic compounds that are employed. The removal of the polycyclic aromatic compounds further contributes to the expense of manufacturing the N-substituted-N'-phenylphenylenediamine. U.S. Pat. No. 4,968,843 discloses a process for the preparation of a N-substituted-N'-phenyl-p-phenylenediamine. The process in this patent involves reacting N-phenyl-p-quinoneimine with a primary amine. This patent teaches that the N-phenyl-p-quinoneimine reactant should not contain more than 5 weight percent p-hydroxydiphenylamine and preferably no or only trace amounts are present. The patent teaches that with an increasing amount of p-hydroxydiphenylamine, there is an increasing hinderance of the reaction to yield the N-substituted-N'-phenyl-p-phenylenediamine. Since demand for N-substituted-N'-phenyl-p-phenylenediamines is on the increase with their wide-spread applications, there is a need for a new and more efficient process for their production.